Camera photometry system

ABSTRACT

This invention relates to a camera photometry system which uses accumulation-type photoelectric elements to output photometry information related to the brightness of the subject field. Its purpose is to provide a camera photometry system which has a simple structure and which contains a two dimensional photometry mechanism with a wide dynamic photometry range. A camera photometry system using this invention is composed of a two dimensional photometry mechanism made of multiple accumulation-type photoelectric elements, and an accumulation control mechanism which controls the accumulation time of the photoelectric elements, with the system structured so that the multiple photoelectric elements are grouped in separate areas and the accumulation control mechanism is positioned at each of these areas and controls the accumulation time of the photoelectric elements in each separate area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a camera photometry system which outputsphotometric information related to the brightness of the subject fieldusing accumulation-type photometry elements.

2. Description of Related Art

Public disclosure of Japanese Laid-Open Publication No. 62-169569discloses a conventional type camera. As shown in FIG. 14, this deviceis equipped with multiple rows (PAL1, PAL2) of one dimensionalphotoelectric elements, multiple rows (FAL1, FAL2) of first chargeaccumulation elements, multiple rows (GAL1, GAL2) of second chargeaccumulation elements, and a transmission register (RG), and isstructured so that the accumulation times of the rows of photoelectricelements (PAL1, PAL2) can be controlled separately.

Because the conventional device described above is limited to onedimension for photometric regions, rows of charge transmission elementsmust added in order to expand the photometric regions to two dimensions.As a result, both rows of charge accumulation elements and rows ofcharge transmission elements are necessary, creating problems includingthe structure becomes complex, costs rise and yield declines.

In addition, until now it has been impossible to obtain optimalphotometric output for subject fields with a large variance inbrightness, such as when a very bright area such as the sky is in theupper part of the field and a dark area such as a forest is located inthe lower part of the field.

SUMMARY OF THE INVENTION

The purpose of this invention is to provide a camera photometry systemwhich has a simple structure and which contains a two dimensionalphotometry mechanism with a wide dynamic photometry range.

A camera photometry system using this invention is composed of a twodimensional photometry mechanism made of multiple accumulation-typephotoelectric elements, and an accumulation control mechanism whichcontrols the accumulation time of the photoelectric elements, with thesystem structured so that the multiple photoelectric elements aregrouped in certain separate areas and the accumulation control mechanismis positioned at each of these areas and controls the accumulation timeof the photoelectric elements in each separate area.

In this case, it would be fine to have these specified areas dividedvertically with respect to the subject field whose light is beingmeasured.

In addition, the two dimensional photometry mechanism is equipped with afirst transmission mechanism which horizontally transmits the chargewhich accumulates in the photoelectric elements and a secondtransmission mechanism which transmits the charge vertically, and isstructured so that it regulates the different accumulation times of eachof the areas by temporarily storing in one of the two transmissionmechanisms charge from areas in which the accumulation time is short.

In addition, the photometry system is equipped with a clock mechanismwhich keeps track of the month, day and year that photographs are taken,and is structured so that the initial accumulation time of thephotometry elements is set based on information from this clockmechanism.

The invention divides the two dimensional photometry mechanism which iscomposed of multiple accumulation-type photoelectric elements intospecified areas, such as an upper area and a lower area with respect tothe subject field, and independently controls in each area theaccumulation time of the photoelectric elements which make up each areaby means of an accumulation control mechanism which is positioned ateach of these areas. Through this, it is possible to achieve optimalphotometric control which agrees with the brightness conditions in eacharea. In addition, the initial accumulation time of the photometryelements is set based on information from a clock mechanism which keepstrack of the date that the photographs are taken.

In addition, when the charge which accumulates in the photoelectricelements is transmitted to the outside by means of a transmissionmechanism, transmission control is achieved without the installation ofa special charge accumulation mechanism because charge from areas withshort accumulation times is temporarily stored in the transmissionmechanism during the time prior to when the accumulation of the chargeis completed in areas with long accumulation times and the charge istransmitted to the transmission mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical system showing the embodiment ofthe invention;

FIG. 2 is a block diagram of a circuit system showing the embodiment ofthe invention;

FIG. 3 is a configuration diagram showing the embodiment of thephotometry element shown in FIG. 1;

FIG. 4 is a configuration diagram of the photometry regions shown inFIG. 3;

FIG. 5 is a detailed configuration drawing of the photometry part shownin FIG. 2;

FIG. 6 is a diagram used to explain the direction of chargetransmission;

FIG. 7 is a diagram used to explain the direction of chargetransmission;

FIG. 8 is a diagram used to explain the positioning of the photoelectricelements;

FIG. 9 is a configuration drawing showing a different embodiment of thephotometry part;

FIG. 10 is a flowchart used to explain the action of the invention;

FIG. 11 is a flowchart showing the initial accumulation time settingprocess subroutine;

FIG. 12 is a flowchart showing the accumulation time setting processsubroutine;

FIG. 13 is a drawing to explain the accumulation time setting; and

FIG. 14 is a drawing to explain conventional photometry systems.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 are block diagrams showing the optical systems and circuitsystems of the first embodiment of a photometry system of the inventionused in an interchangeable lens camera that uses photographic film.

The optical system shown in FIG. 1 is structured so that light rayspassing through the photography lens 1 are reflected by a quick returnmirror 2, creating an image on a diffusion screen 3, and reach the eyeof the photographer by passing through a condenser lens 4, a pentagonalprism 5 and the eyepiece lens 6. In addition, some of the light rayswhich formed the image on the diffusion screen 3 pass through thecondenser lens 4, the pentagonal prism 5, a photometry prism 7 and aphotometry lens 8 to form an image on a photometry element 9.

The photometry element 9 is made up of 273 photometry regions dividingthe subject field into 13 rows horizontally and 21 columns vertically,as shown in FIG. 3, and a number is associated with each of thesephotometry regions, with the photometry region in the lower left cornerbeing (1,1) and the photometry region in the upper right corner being(21,13). In addition, each of these photometry regions is divided intothe primary colors red (R), green (G), and blue (B), as shown in FIG. 4,so that 273 photometry values for each of the colors red, green and blueis output from the photometry element 9.

The circuit system, shown in FIG. 2, is a system which calculates theoptimal exposure value based on the photometry value measured by thephotometry element 9 and controls the exposure based on the optimalexposure value. The circuit system is equipped with a photometry part 10which includes the photometry element 9. The photometry part 10 isdivided into a first photometry area 10a and a second photometry area10b, and is structured so that each of the first and second photometryareas 10a, 10b is independently controlled by a control mechanism aswill be described hereafter.

The photometry value which is output from the photometry part 10 isconverted into a digital signal by an A/D converter 11, and the digitalsignal is output to the brightness calculator 12 as digital photometryinformation. The brightness calculator 12 reads information about thepositioning of the exit pupil and the F release value of the photographylens from a lens ROM 13 mounted inside the photography lens, andcalculates a brightness value for each photometry region based on thisinformation and the photometry information. An exposure calculator 14calculates the optimal exposure value based on the output of thebrightness calculator 12, and an exposure controller 15 controls theexposure in accordance with the optimal exposure value through fulldepression of a shutter release button (not shown in figure).

The photometry information from the photometry regions which wasconverted to a digital signal by the A/D converter 11 is supplied to afirst accumulation control part 16, which controls the accumulation timeof the first photometry area 10a, and to a second accumulation controlpart 17, which controls the accumulation time of the second photometryarea 10b. A description of the first and second accumulation controlparts 16,17 will be given hereafter.

In addition, the photometry system is equipped with a clock mechanism 18designed as a timer to keep track of the current date and time. Dateinformation from the clock mechanism 18 is supplied to the first andsecond accumulation control parts 16,17 as information showing the dateand time the photograph is taken, and is used in the process which setsan initial accumulation time which will be described hereafter.

FIG. 5 is a diagram showing further details of the structure of thephotometry part 10. As described above, because each of the 273individual photometry regions in the photometry element 9 is configuredto separately measure the amount of the three primary colors red, greenand blue in the photometry part 10 accumulation-type photoelectricelements Rij, Gij, and Bij (where i=1, 2, . . . , 21; j=1, 2, . . . ,13) which are positioned in the horizontal direction in positionscorresponding to each photometry region.

In addition, horizontal transmission registers H1,H2 . . . ,H13 aresituated at each of the 13 rows of photoelectric elements, and theoutput end of each of the horizontal transmission registers H1-H13 isconnected in parallel to a vertical register V1.

Because the photometry part 10 is divided into a first photometry area10a and a second photometry area 10b as described above, registers H1-H7are registers for the first photometry area 10a and registers H8-H13 areregisters for the second photometry area 10b. The device is configuredso that the starting and stopping of accumulation in each of theaccumulation-type photoelectric elements in the respective areas iscontrolled independently by the first accumulation control part 16 andthe second accumulation control part 17, respectively.

Next, we will explain the action of the photometry part 10. The electriccharge which accumulates in the photoelectric elements Rij,Gij,Bij ineach of the photometry regions is transferred to the correspondinghorizontal transmission register H1-H13 upon the generation of anaccumulation termination signal by whichever of the accumulation controlparts 16 or 17 that corresponds to the element. Furthermore, the chargefrom areas with short accumulation times is stored in the horizontaltransmission register until the accumulation of charge is terminated inareas with long accumulation times and the charge is transmitted to thehorizontal transmission register.

When the charge accumulated in all of the photoelectric elementsRij,Gij,Bij has been transmitted to the horizontal transmissionregisters H1-H13, it is transmitted to the vertical register V1 oneelement at a time in accordance with a clock signal produced in thephotometry part 10. The vertical register V1 transmits the charge to theA/D converter 11 via an output circuit (not shown in the diagram) in thephotometry part 10 also in accordance with an internal clock.

By thus dividing the photometry part 10 into areas and controlling theaccumulation time of the photoelectric elements in each area, it becomespossible, for instance in the case when the upper section of the subjectfield H is bright while the lower section is a darker scene, to bringthe photometric output of the two areas within the range wherephotometry is possible and it also becomes possible to enlarge thedynamic photometry range by making the accumulation time of thephotometry regions in the lower section longer than the accumulationtimes of the photometry regions in the upper section.

We will further explain this point using FIG. 6. Suppose a subject O ispresent as shown in FIG. 6. Light rays passing through the photographylens 1 form an image of the subject O' on the screen 3, and this imageO' is projected onto the photometry element 9 through the photometrylens 8, thereby forming another image O".

In this case, taking the direction of transmission in the verticalregister V1 of the photometry part 10 to be in the direction of thearrow A, in other words from the top (upper side) to the bottom (lowerside) with respect to the subject field H, because the charge from theelements in the relatively dark lower side are transmitted withoutpassing through the relatively bright upper side when the charge istransmitted by the vertical register V1, it is possible to eliminate thesmear phenomenon which occurs when the charge from the brighter sectionsof the screen flows into the photometric charge from the less brightsections.

In other words, because it is common for bright regions such as the skyto be positioned in the upper part of the subject field H, such as isshown in FIG. 7, it is possible to eliminate the smear phenomenonbecause by having the direction of transmission be in the direction ofarrow A from the upper side to the lower side, charge from the darklower regions does not pass through the bright upper regions.

Concerning the positioning of the photoelectric elements, the opticalaxis passes through the center of photoelectric element G11,7 used forgreen light in the photometry region numbered (11,7), as shown in FIG.8. Because the transmission mechanism is located on the light receptorsurface in accumulation-type photoelectric elements, the aperture ratio,which is the ratio of the photoelectric part to the light receivingarea, unavoidably decreases. As a result, it becomes impossible tomeasure light from objects outside the photoelectric part. Because ofthe high probability that the major subject will be located on theoptical axis on the photographic screen, it is vital that thephotoelectric part be on the optical axis. In addition, when pixels usedto measure different color tones are lined up alternately, the pixelwhich measures the color green, which has a sensitive distributionnearest the human visibility curve, must be located on the optical axisin order to improve the photometric accuracy.

As an alternative example of the photometry part 10, when a frametransfer format is used in which the photometry elements 9 are separatedinto light receptors P and accumulators M, as shown in FIG. 9, it ispossible to eliminate the smear phenomenon by having the direction ofcharge transmission be from the upper side to the lower side because thecharge is transmitted to the accumulators M via the light receptors P.

Next, we will explain the action of the photometry system in theembodiment by referring to the flowchart shown in FIG. 10. The action isinitiated by depressing the shutter button (not shown in the diagram)halfway.

First, the process of setting the initial accumulation time is executed(step S1). This process sets the initial accumulation time ta of thephotoelectric elements Rij,Gij,Bij from the date and time of thephotograph. Details of the process of step S1 with be explained byreferring to the flowchart shown in FIG. 11 at a later time.

Next, accumulation of charge is executed in the first and secondphotometry areas 10a, 10b through the accumulation time ta which hasbeen set, and the photometry value obtained as a voltage signal fromeach of the photometry regions is converted into a digital signal by theA/D converter 11 and output as digital photometry information (step S2).

Next, a brightness value is calculated by the brightness calculator 12based on the digital photometry information, the accumulation time taand information from the lens ROM 13 (step S3). The exposure calculator14 then calculates the optimal exposure value based on the calculatedbrightness value (step S4). Because the method of calculating theoptimal exposure value is explained in detail in the public disclosureof Japanese Laid-Open Publication No. 4-310930, which corresponds toU.S. patent application Ser. No. 07/831,201, the disclosure beingincorporated by reference herein, a detailed explanation is omitted.

Next, the system determines whether the shutter button (not shown) hasbeen depressed all the way (step S5). If it is depressed all the way,the exposure is controlled by the exposure controller 15 based on theoptimal exposure value (step S6), and the process terminates. If theshutter button is not depressed all the way, the next accumulation timeta is set (step S7) and the process is repeated from step S2. Theprocess involved in step S7 will be explained hereafter.

First, we will explain the initial accumulation time setting processsubroutine (of step S1) by referring to the flowchart shown in FIG. 11.In step S11, the current date and time are input by means of the clockmechanism 18, and the probable outdoor conditions are divided into thethree categories of "daytime", "morning or evening" and "night" basedupon the information. When it is determined that night conditions exist(step S12), the initial accumulation time ta is set at 160 ms (stepS13). When a standard photometric optical system and photometry elementare used, this corresponds to measuring light with a brightness of EV1.

If the determination is not "night" in step S12, the system determineswhether "morning or evening" conditions are probable (step S14). If thedetermination is "morning or evening", the initial accumulation time tais set at 20 ms (step S15). With the photometry system mentioned above,this corresponds to measuring light with a brightness of EV4.

If the determination is not "morning or evening" in step S14, thedetermination is "daytime", so the initial accumulation time ta is setat 2.56 ms (step S16). With the photometry system mentioned above, thiscorresponds to measuring light with a brightness of EV7.

Next, we will explain the accumulation time setting process subroutine(of step S7) by referring to the flowchart shown in FIG. 12. First,average values ADa,ADb are calculated for the digital photometryinformation from each of the photometry regions in the first photometryarea 10a and the second photometry area 10b (step S21). The averagevalues ADa,ADb are within the range 0-1,023. The values are the outputof the A/D converter 11. The A/D converter 11 has a level ofdiscrimination of 10 bits so there are 1024 values. In this application,minimal amounts of data are assigned a value of zero. Thus, the highestvalue is 1023 and the range 0-1,023. The minimal value is zero becauseit cannot be measured. If assigned the value 1, it could be read asone-half of the value 2. However, the value 1 is used to represent theminimum amount of measurable data.

Then, it is determined whether the average value ADa from the firstphotometry area 10a is zero (step S22). If the average value ADa iszero, the next accumulation time ta is set at 1,024 times the previousaccumulation time ta (step S23). This is because data which was "1",that is, the minimum measurable amount of light, in the previousmeasurement of light in the next measurement becomes the value that justexceeds the maximum value "1,023" and data less than or equal to thisends up within the photometry range, which is very convenient.

If it is determined in step S22 that the average value ADa is not zero,it is determined whether or not the average value ADa is the maximummeasurable value "1,023", values above "1,023" being overflow values andrepresented by "1,023" (step S24). If it is determined that the value isthe maximum value, the next accumulation time ta is set at 1/1024 timesthe previous accumulation time (step S25). This is because data thatoverflowed, in the previous light measurement becomes "1", the smallestor minimum amount of light in the next measurable light measurement anddata greater than or equal to this ends up within the photometry range,which is very convenient.

If it is determined that the average value ADa is not the maximum value,the next accumulation time ta is found using the following equation(step S26):

    ta=ta×32/ADa.                                        (eq. 1)

Having done this, the setting of the next accumulation time ta for thefirst photometry area 10a is concluded.

We will now discuss the method of setting the accumulation time byreferring to FIG. 13. The graph of FIG. 13 shows the value of thedigital photometry information on the horizontal axis with the frequency(number) of photometry information in all of the photometry regions inthe first photometry area 10a shown on the vertical axis.

In the graph, when the average value ADa of the photometry informationis "16", for instance, the next accumulation time ta determined fromequation 1 becomes double the previous accumulation time ta, and if thecondition of the subject does not change, the next average value ADawill be "32." In addition, when the average value ADa is "64", the nextaccumulation time ta determined from equation 1 becomes one-half theprevious accumulation time ta and, if the condition of the subject doesnot change, the next average value ADa will be "32." That is to say, ifthe brightness of the subject does not change, the next average valuewill always be "32." This is because the brightness value is expressedas a logarithm, so when the average value is "32" in the range from "0"to "1023", the photometry range can be secured with exactly 5EV both upand down.

Then, when the setting of the next accumulation time ta in the firstphotometry area 10a is concluded, the next accumulation time tb in thesecond photometry area 10b is set. Because the method of setting theaccumulation time tb is the same as the method of setting theaccumulation time ta discussed above, a detailed explanation is omittedhere, but first, it is determined whether the average value ADb from thesecond photometry area 10b is zero (step S27), and if ADb=0, the nextaccumulation time tb is set at 1024 times the previous accumulation time(step S28).

If the average value ADb is not zero, it is determined whether or notthe average value ADb is the maximum value "1,023" (step S29), and if itis this maximum value, the next accumulation time tb is set at 1/1024times the previous accumulation time (step S30). If it is determinedthat the average value ADb is not the maximum value, the nextaccumulation time tb is found using the following equation (step S31):

    tb=tb×32/ADb.                                        (eq. 2)

Having done this, the setting of the next accumulation time tb for thesecond photometry area 10b is concluded.

By thus dividing accumulation-type photometry elements into multipleareas and separately controlling the accumulation time in each area withthis invention, it becomes possible to always obtain the optimalphotometry output even in relation to subject fields from which lightcould not be measured before because of a large difference inbrightness, thereby enlarging the dynamic photometry range.

In addition, when the accumulation time varies in each of the areas, itbecomes possible to control transmission without the installation of aspecial charge accumulation mechanism because charge from areas withshort accumulation times is temporarily stored in the transmissionmechanism until the accumulation of charge is completed in areas withlong accumulation times.

What is claimed is:
 1. A camera photometry system, comprising:a twodimensional photometry mechanism made up of a plurality ofaccumulation-type photoelectric elements; and an accumulation controlmechanism for controlling an accumulation time for a charge in saidaccumulation-type photoelectric elements, wherein said accumulation-typephotoelectric elements are grouped in certain separate areas and saidaccumulation control mechanism has a control element for each of saidcertain separate areas to separately control the charge accumulationtime of the accumulation-type photoelectric elements therein, whereinthe separate control elements control the charge accumulation times forsaid certain separate areas to be different from one another.
 2. Thecamera photometry system as described in claim 1, wherein said certainseparate areas that are created by dividing vertically said photometrymechanism relative to a subject field whose light is being measured. 3.The camera photometry system as described in claim 1, wherein said twodimensional photometry mechanism is equipped with a first transmissionmechanism which horizontally transmits the charge which accumulates insaid accumulation-type photoelectric elements and a second transmissionmechanism which vertically transmits the charge, and said twodimensional photometry mechanism regulates different accumulation timesof each of said certain separate areas by temporarily storing in one ofsaid first and second transmission mechanisms the charge from areas inwhich accumulation time is short.
 4. The camera photometry system asdescribed in claim 1, wherein light rays from the subject field aredirected to the certain separate areas that define multiple photometryareas of the photometry mechanism by a single photometric opticalsystem.